Forget distribution channel, many retailers avoid AWS so they don't funnel money into a competitor.
Not just money, but data also
The idea that a marketplace could turn around and sell their own products that directly compete with third party sellers is insane. Come to think of it, I assume Walmart would fall into this problem as well.
Amazon is more similar to a flea market organizer that sets up their own massive both. They can put their items in front of customers first and decide what to sell based upon what they see people carry away.
You'd think the government would be the Goliath in this battle, but it's the other way around. FTC is more of a nuicanse than an actual problem, and it's gonna remain that way for as long as FTC keeps operating on a shoestring budget.
Don't conflate AWS with the Amazon Sellers program.